This invention relates to radio communications and more specifically to multilevel power amplifiers used in radio frequency (RF) communications transmitting equipment.
RF power amplifiers are used in military and commercial applications to increase transmitted power levels to meet communications systems requirements. Many applications require multiple power levels due to differing transmit range requirements. Some applications require a RF power amplifier to operate at three power levels such as high, medium, and low.
Present approaches of obtaining multiple power levels from a power amplifier involve switching the signal path around the high power stages. These approaches require the use of high power RF switches typically implemented with PIN diodes and quarter wave lines. These high power RF switches are costly, have poor reliability, and reduce the efficiency of the RF power amplifier. Another disadvantage of using high power PIN diode RF switches is that a modulated amplifier at the input of the power amplifier sees impedance changes on its output in the different power modes. The modulated amplifier transmits into either a splitter network or a bypass path and since the design of the modulated amplifier is dependant on the output load, there is a comprise in the design to satisfy all load situations.
What is needed is a power amplifier capable of delivery multiple power levels at low cost, with good efficiency, and with good modulation performance and spectral quality.
A power amplifier with multiple power modes for providing a desired output power level is disclosed. The power amplifier has an input amplifier stage for amplifying an input signal. A splitter network is connected to the input amplifier stage for splitting the amplified input signal into splitter output signals. Switches connected to the splitter network select desired splitter output signals. Power amplifier stages connected to the switches amplifying the desired splitter output signals into amplified output signals. A bypass network provides a bypass path around the power amplifier stages. A combiner network connected to the power amplifier stages and to the bypass network combines the amplified output signals and the bypass signal to obtain the desired power output level. The splitters and combiners are 3-dB hybrids.
The power amplifier splitter network further comprises an input splitter for splitting the input signal. The input splitter has an input port connected to the input amplifier for receiving the amplified input signal and an isolation port connected to a termination. A first splitter in the splitter network provides splitter output signals and has an input port connected to a 90-degree port of the input splitter and an isolation port connected to a termination. A second splitter also provides splitter output signals and has an input port connected to a 0-degree port of the input splitter and an isolation port connected to the bypass network.
The switches in the power amplifier further comprise a first switch connected to a 90-degree port of the first splitter for selecting the desired splitter output signals. A second switch is connected to a 0-degree port of the first splitter for selecting the desired splitter output signals. A third switch is connected to a 0-degree port of the second splitter for selecting the desired splitter output signals. A fourth switch is connected to a 90-port of the second splitter for selecting the desired splitter output signals.
The power amplifier stages comprise four power amplifier stages. A first power amplifier stage is connected to the first switch for amplifying the desired splitter output signals into the amplified output signals. A second power amplifier stage is connected to the second switch for amplifying the desired splitter output signals into the amplified output signals. A third power amplifier stage is connected to the third switch for amplifying the desired splitter output signals into the amplified output signals. A fourth power amplifier stage is connected to the fourth switch for amplifying the desired splitter output signals into the amplified output signals.
The bypass network may be a hybrid coupler directional switch. The hybrid directional switch comprises a third splitter with an isolation port connected to a termination and an input port connected to an isolation port of the second splitter to receive and split the bypass signal. A first switch is connected to a 0-degree output port of the third splitter for switching the split bypass signal. A second switch is. connected to a 90-degree output port of the third splitter for switching the split bypass signal. A third combiner has an input port connected to an output of the first switch for receiving the split bypass signal, an isolation port connected to an output of the second switch for receiving the split bypass signal, a 0-degree output connected to a termination, and a 90-degree output port for outputting the combined bypass signal.
The power amplifier combiner network further comprises a first combiner with an input port connected to the first power amplifier stage, an isolation port connected to the second power amplifier stage, and a 90-degree port connected to a termination. The first combiner combines the amplified output signals. A second combiner has with an input port connected to the third power amplifier stage, an isolation port connected to the fourth power amplifier stage, and a 0-degree port connected to a termination. The second combiner combines the amplified output signals. An output combiner has with an input connected to a 0-degree port of the first combiner, an isolation port connected to a 90-degree port of the second combiner, and a 0-degree port connected to a termination. The output combiner further combines the amplified output signals. A coupler with an input port connected to a 90-degree port of the output combiner receives the combined amplified output signals, a coupled port connected to the 90-degree port of the third combiner receives the bypass signal, and an output port provides the desired power output level.
Another embodiment of the power amplifier may comprise two power amplifier stages. A first power amplifier combiner combines the desired splitter output signals. The first power amplifier combiner has an input port connected to the first switch, an isolation port connected to the second switch, and a 90-degree port connected to a termination. A second power amplifier combiner combines the desired splitter output signals. The second power amplifier combiner has an input port connected to the third switch, an isolation port connected to the fourth switch, and a 0-degree port connected to a termination. A first power amplifier stage amplifies the first power amplifier combiner output and is connected to a 0-degree port of the first power amplifier combiner. A second power amplifier stage amplifies the second power amplifier combiner output and is connected to a 90-degree port of the second power amplifier combiner.
The bypass network of the power amplifier with two power amplifier stages also may be a hybrid coupler directional switch. A third splitter receives the bypass signal and splits it. A pair of switches connected to the third splitter outputs switch the bypass signal. A third combiner connected to the pair of switches recombines the bypass signal and outputs the bypass signal.
The two-stage power amplifier combiner network comprises an output combiner with an input connected to the first power amplifier stage, an isolation port connected to the second power amplifier stage, and a 90-degree port connected to a termination. The output combiner combines the amplified output signals. A coupler with an input port connected to a 0-degree port of the output combiner receives the combined amplified output signals, a coupled port connected to a 90-degree port of the third combiner for receives the bypass signal, and an output port provides the desired power output level.
It is an object the present invention to provide a power amplifier capable of delivery multiple power levels at low cost, with good efficiency, and with good modulation performance and spectral quality.
It is an advantage of the present invention to eliminate the need for high power RF switches.
It is an advantage of the present invention to provide a multilevel power amplifier with a bypass path with high isolation from the main path.
It is an advantage of the present invention that no bypass path is used in a medium power mode.
It is a feature of the present invention to provide a multilevel power amplifier with a modulated stage that transmits into the same load for each power level.